Method of curtain-coating an adhesive material on a structural part

ABSTRACT

A method and apparatus for applying an adhesive material onto a heavily contoured surface of a structural part including the step of heating the contoured surface to a predetermined temperature level. The contoured surface is then passed through a vertical continuously falling curtain of adhesive material at a speed to deposit a desired uniform coating on the heated contoured surface. The heated surface causes a substantial portion of the liquid solvent of the adhesive to rapidly vaporize to substantially increase the viscosity of the adhesive.

United States Patent [191 Wentroble et al.

[ 51 Oct. 29, 1974 METHOD OF CURTAIN-COATING AN ADHESIVE MATERIAL ON A STRUCTURAL I PART [75] Inventors: Dale E. Wentroble, Tyler, Tex.;

Milton H. Coleman, East Syracuse,

[73] Assignee: Carrier Corporation, Syracuse, NY. [22] Filed: July 7, 1972 21 Appl. No.: 269,679

[52] US. Cl 156/307, 29/454, 92/34, 92/47, 117/47 H, 117/104 R, 1l7/l05.3,

117/120, 118/314, 118/315, l18/DIG.4, 156/322 [51] Int. Cl C09j 5/00, B44d 1/09, B05c 5/00 [58] Field of Search 117/104 R, 105.3, 120, 117/47 H; 156/307, 322; 118/315, 314, DlG..

[56] References Cited 7 UNITED STATES PATENTS 2,779,690 l/1957 Gaiser 117/104 2,972,553 2/1961 Hess 117/47 H 3,067,060 12/1962 Glaus 117/102 3,341,354 9/1967 Woods et al 1 17/1053 3,461,840 8/1969 Turner 118/314 3,468,099 9/1969 Vogt 53/140 3,477,126 l1/l969 Price 29/605 3,524,759 8/1970 McConnell et al. ll7/l05.3 3,632,403 l/l972 Greiller 1l7/l05.3

Primary Examiner-Charles E. Van Horn Assistant Examiner-Robert A. Dawson Attorney, Agent, or Firm-J. Raymond Curtin; Barry E. Deutsch [5 7] ABSTRACT A method and apparatus for applying an adhesive material onto a heavily contoured surface of a structural part including the step of heating the contoured surface to a predetermined temperature level. The contoured surface is then passed through a vertical continuously falling curtain of adhesive material at a speed to deposit a desired uniform coating on the heated contoured surface. The heated surface causes a substantial portion of the liquid solvent of the adhesive to rapidly vaporize to substantially increase the viscosity of the adhesive.

1 Claim, 2 Drawing Figures METHOD OF CURTAIN-COATING AN ADHESIVE MATERIAL ON A STRUCTURAL PART BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for applying adhesive onto a heavily contoured surface. More particularly, this invention relates to a method and apparatus for applying adhesive material onto a concave surface whereby an elastomeric bellows may be subsequently permanently bonded thereto.

There are many varied processes by which an adhesive material may be applied onto a surface of an object. For example, the object may be dipped directly into a pool or bath of the adhesive material. A further method includes the step of brushing or rolling the adhesive material onto the surface of the object.

Each of the foregoing processes suffer from one or more disadvantages. A dipping process is performed at relatively slow speeds and is therefore undesirable for applications requiring high speed operation. In addition, a dipping process does not readily provide a uniformly consistent coating of adhesive on successive obects.

Brushing and rolling processes also suffer from relatively slow speed operation. In addition, they also do not readily provide a uniformly consistent coating of adhesive material on successive objects.

To overcome the foregoing defects and disadvantages in the prior art, a curtain coater of a type disclosed in U.S. Pat. No. 3,067,060, issued Dec. 4, 1962, in the name of Bernhard Glaus and assigned to Ulrich Steinemann AG. Ltd., has been increasingly employed in many applications where high speed operations and a uniform, adhesive coating are requirements to satisfy the needs of the particular process. A curtain coating apparatus of the type disclosed in the aforecited patent is marketed in the United States by the Ashdee Division of George Koch Sons, Inc. of Evansville, Indiana.

Briefly, a curtain coater functions in the following manner. The adhesive material is maintained in a liquid state and is discharged from a pressurized container in an unbroken substantially vertical curtain. The object upon which it is desired to have the adhesive material deposited, is conveyed through the curtain at a speed to obtain a desired coating thickness. The adhesive ma terial which is not deposited on the objects is recovered in a sump from whence the adhesive material is recycled. Relatively low viscous adhesive materials are generally employed in the above described process. The process has proven to be particularly satisfactory for applying an adhesive material onto a generally flat surface.

However, the process has not proven to be as adaptable for use in applying adhesive materials on objects having a heavily contoured or non-planar surface. For example, if the surface is concave, the adhesive material, due to its relatively low viscosity, has a tendency to flow down the inclined sides of the concave surface and collect at the bottom of the concavity. As is obvious, an inconsistent, non-uniform coating of adhesive is thus obtained.

Additionally, it has been determined the thickness of the coating on substantially vertical sides of a contoured surface has been generally inconsistent. Such vertical sides are parallel to the vertically falling curtain; adhesive material contacting the top of such sides generally flows down the surface thereof. This sometimes results in the production of void areas at the top of generally vertical surfaces.

A further problem involving the utilization of curtain coaters relates to the temperature and relative humidity of the ambient air in the environment in which the process apparatus is installed. As noted before, the process utilizes adhesive materials in a liquid state. The solvents employed in the adhesive materials are generally extremely volatile. They will flash or vaporize upon contacting the surface of the object being adhesively coated, absorbing heat therefrom. If the temperature of the ambient air is above the resulting temperature of the object, the air passing in heat transfer relation with the object will lose heat thereto. If the air has a high relative humidity, the temperature of the air may fall below its dewpoint upon its losing heat to the object and thus condensate may form on the surface of the object. A layer of moisture, no matter how thin, is extremely harmful to the quality of the ultimate bond fonned between the object and the second article being bonded thereto. Thus, it has, in many instances, been necessary to place the curtain coating apparatus in a controlled environment to thereby prevent the temper ature of the air from ever falling below the dewpoint. As is obvious, the apparatus necessary to maintain a controlled atmosphere substantially increases the cost of installing the process.

SUMMARY OF THE INVENTION It is therefore an object of the invention to obtain a uniformly consistent adhesive coating on heavily contoured surfaces.

It is a further object of this invention to prevent the formation of condensate in an uncontrolled environment on a surface which is to be adhesively coated.

It is still another object of this invention to achieve a uniform coating on a contoured surface that is disposed parallel to the vertically falling curtain.

It is yet a further object of this invention to achieve a high quality bond between a concave metallic surface and an elastomeric material.

It is still a further object of this invention to improve curtain coating apparatus. These and other objects of the invention are obtained by heating the surface of the object prior to its having the adhesive material deposited thereon by being conveyed through a falling curtain of the material. The heated surface causes a substantial portion of the liquid solvent to rapidly vaporize to substantially increase the viscosity of the adhesive material. The resulting highly viscous adhesive will remain where initially deposited on the contoured surface.

In addition, heating the surface will prevent any condensate from forming thereon. The surface is heated to a temperature level that will remain in excess of the temperature of the ambient air regardless of the withdrawal of heat therefrom by the vaporization of any solvent.

Furthermore, in order to overcome the problem of non-uniform or inconsistent coating thickness on a vertical side of a contoured surface, an additional quantity of adhesive material is directed at such vertical side in a generally diagonal direction to the vertically falling curtain.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically represents a process for applying adhesive material in accordance with our invention; and

FIG. 2 is a perspective illustration of a heavily contoured surface that is particularly suitable for processing in our invention, a portion of the process components also being shown in perspective.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, there is shown a preferred embodiment of our invention. FIG. 1 schematically illustrates a process that has proven highly satisfactory for applying adhesive material quickly and uniformly onto an object having a heavily contoured or non-planar adhesive-receiving surface.

Process 10 preferably includes a first station 11, whereat the object being adhesively coated may be cleaned to remove any foreign matter from the surfaces thereof. With reference to FIG. 2, there is shown a perspective view of an object 12 having a heavily contoured or non-planar surface, such as concave portion 13. Concave portion 13 includes opposed generally vertical side walls 14 and 15 and generally arcuate portion 16 which connects the side walls. The process to be more fully explained hereinafter, shall be described as applying a uniform adhesive coating on the surfaces defining concave portion 13. However, the process is equally suitable for applying a uniform coating on other non-planar surfaces and therefore should not be limited for use only with the particular illustrated non-planar surface.

Process 10 further includes a pre-heat station 17 through which object 12 is conveyed subsequent to its being cleaned. Station 17 may include an infra-red heater of a type familiar to those skilled in the arts. It has been found that maintaining the object within the heater for about 15 seconds at a temperature of approximately l75F increases the temperature of the object to a desired level for a reason to be more fully explained hereinafter.

From the heater, object 12 is then conveyed through a curtain coater 18 of a type sold by the Ashdee Division of George Koch Sons, Inc. of Evansville, Indiana. Curtain coater 18 preferably includes a first transport 19, a second transport 20, a sump 21, and a supply head 22.

Object 12, upon which it is desired to place an adhesive coating, is guided onto continuously moving transport 19. The object is then conveyed through a continuously vertical falling curtain of liquid adhesive material 29 (see FIG. 2). In the preferred embodiment, object 12 is to have an elastomeric bellows subsequently bonded thereto. Therefore, an adhesive material particularly suitable for joining an elastomeric material to a metal is preferably employed. The adhesive material may include thermoset resins and neoprene suspended in volatile solvents such as hexane and toluene. A particularly suitable adhesive material is sold by the B. F. Goodrich Co. under the tradename A862B."

As is illustrated in FIG. 2, the liquid adhesive curtain is supplied under pressure from header 22 in an unbroken, substantially rectangular configuration. Object 12 is conveyed through the adhesive curtain at a predetermined speed, whereby a desired coating thickness is obtained on the surface of the object. With particular reference to FIG. 2, it is only desired to place the adhesive coating on the surface of concave portion l3. Therefore, the width of the falling adhesive curtain is limited (by suitable means not shown) by the width of concave portion 13.

The adhesive material which is not deposited on the surface of the object falls into sump 21 where it is recovered for recycling back to head 22. The adhesive material in sump 21 is continuously pumped, via conduit 23, to head 22. If a more detailed explanation of the curtain coating apparatus is desired, reference may be had to previously cited US. Pat. No. 3,067,060.

Head 22 includes first and second tubes 24 and 25 which are connected to a supply header 26. A portion of the adhesive material is dispensed via the tubes in a generally diagonal direction to the falling curtain of adhesive and, in addition, in a generally opposed direction to the moving object, for a reason to be more fully explained hereinafter.

Object 12 is conveyed by second transport 20 to the end of the adhesive coating station, from whence the object is moved into a drying station 27. Drying station 27 may include infrared heating means which cooperate with a high velocity flow of hot air to carry off the solvent of the adhesive material from the coating on the object's surface. It has been found that an operating temperature of 400F eliminates substantially all of the solvent remaining on the objects surface. The object is then stored at a station (not shown) for a period of time to permit the solid components of the adhesive material to become permanently affixed to the objects surface.

As noted before, curtain coating has been found to be a particularly suitable process for obtaining a substantially uniform, consistent coating on a generally flat surface. However, heretofore the curtain coating process has not proven equally suitable for use in applications where the object being coated includes heavily contoured or non-planar surfaces.

In order to obtain the continuous falling liquid curtain of adhesive material, it has been generally necessary to use a low viscous adhesive material. With reference to FIG. 2, the low viscous adhesive material does not always remain where it initially contacts the surface of object 12. The adhesive material exhibits a tendency to flow down the sides of walls 14 and 15 and collect at the central part of arcuate portion 16. As is obvious, the required uniform consistent coating would not be obtained.

By pre-heating the object upon which the coating is to be applied, for example, at station 17, the volatile solvents will essentially vaporize upon contacting the surface of the object, thereby almost instantaneously substantially increasing the viscosity of the adhesive. The adhesive material thus has a tendency to remain on the portion of the non-planar surface at which it initially contacts the object.

A second problem pre-heating the object obviates is related to the formation of condensate upon the objectss surface. As noted previously, the solvents employed in the composition of the adhesive material are generally extremely volatile. As such, even without preheating, a portion thereof will vaporize or flash upon contacting the relatively warm surface (at ambient air temperature). The vaporization of the solvents will decrease the surface temperature of the object by removing heat therefrom during the solvents change of state.

If the air in the environment in which the process is installed is at a high relative humidity, the cooling thereof by passing in heat transfer relation with the surface previously cooled by the flashing of the solvents may result in the temperature of the ambient air decreasing below its dewpoint. Condensation may thus occur on the surface of the object which is to be coated. Water greatly decreases the quality of any adhesive bond which may subsequently be obtained. Preheating the object to a sufficient temperature level prevents the formation of condensate. Irrespective of any flash cooling of the surface, the temperature thereof will be maintained above the ambient temperature. Pre-heating the object thereby solves two problems heretofore found in applications using a curtain coater to apply a coating on a non-planar surface.

A further problem has been noted whence any of the surfaces to be coated are disposed in a vertically extending direction. As such, they are parallel to the path of movement of the falling curtain. It has been noted that an inconsistent, non-uniform coating would be obtained on such surfaces; it being assumed the reason therefore is the coating material slides down the vertical surfaces due to its own weight and its relatively low viscosity.

With reference to H0. 2, tubes 24 and 25 are provided to overcome the foregoing difficulty. The tubes direct a portion of the adhesive material against the surfaces of sides 14 and 15. The flow of adhesive material from the tubes is directed in a generally diagonal path relative to the curtain of material falling from head 22. The combination of impingement on the surfaces of the vertically extending sides plus pre-heating to increase the viscosity results in a uniform coating being obtained on all the surfaces of concave portion 13.

As noted previously, it is desirable to bond an elastomeric material to concave portion 13 of object 12.

After object 12 has been satisfactorily coated, the elastomeric material is conveyed through the process. However, since the material in a preferred embodiment is generally flat, the pre-heating step may be eliminated. Also, the additional flow of adhesive material directed at the object via tubes 24 and 25 is no longer required.

After the elastomeric material has a uniform consis tent adhesive coating provided thereon, the two objects are placed in suitable means, such as press 28, whereby the objects are permanently bonded to form an integral assembly.

While we have described and illustrated a preferred embodiment of our invention, our invention should not be limited thereto, but may be otherwise embodied within the scope of the following claims.

We claim:

1. A method of bonding an elastomeric bellows onto a concave metallic surface comprising the steps of:

a. cleaning the concave metallic surface;

b. heating the cleaned surface to a desired temperature level;

c. conveying the heated surface through a vertical continuously falling curtain of a liquid adhesive material at a speed to deposit a desired uniform coating of adhesive material on the concave metallic surface, the heated surface causing a substantial portion of the liquid solvent of the adhesive material to rapidly vaporize to substantially increase the viscosity of the adhesive material;

(1. depositing an additional quantity of adhesive material on the concave surface by directing the additional quantity in a generally diagonal path relative to the continuously falling curtain of liquid adhesive material, the additional quantity of adhesive material being directed at portions of the concave surface which are disposed in a generally vertically extending plane;

e. drying the concave surface to permanently affix the adhesive material coating thereon;

f. cleaning the bellows;

g. conveying the cleaned bellows through the vertical, continuously falling curtain of liquid adhesive material at a speed to deposit a desired thickness of adhesive material on a surface of the bellows;

h. at least partially drying the bellows to permanently affix the adhesive material thereon; and

i. uniting the surface of the bellows having the adhesive material coating thereon with the adhesive material coated concave surface to form a permanent bond therebetween. 

1. A method of bonding an elastomeric bellows onto a concave metallic surface comprising the steps of: a. cleaning the concave metallic surface; b. heating the cleaned surface to a desired temperature level; c. conveying the heated surface through a vertical continuously falling curtain of a liquid adhesive material at a speed to deposit a desired uniform coating of adhesive material on the concave metallic surface, the heated surface causing a substantial portion of the liquid solvent of the adhesive material to rapidly vaporize to substantially increase the viscosity of the adhesive material; d. depositing an additional quantity of adhesive material on the concave surface by directing the additional quantity in a generally diagonal path relative to the continuously falling curtain of liquid adhesive material, the additional quantity of adhesive material being directed at portions of the concave surface which are disposed in a generally vertically extending plane; e. drying the concave surface to permanently affix the adhesive material coating thereon; f. cleaning the bellows; g. conveying the cleaned bellows through the vertical, continuously falling curtain of liquid adhesive material at a speed to deposit a desired thickness of adhesive material on a surface of the bellows; h. at least partially drying the bellows to permanently affix the adhesive material thereon; and i. uniting the surface of the bellows having the adhesive material coating thereon with the adhesive material coated concave surface to form a permanent bond therebetween. 